Long-term follow up of patients with mesothelioma treated with dendritic cell therapy in three phase I trials.

Abstract

2618 Background: Immunotherapy targeting PD-(L)1 has become indispensable in the treatment of many malignant tumors. Recently, checkpoint inhibition using anti-PD-1 in combination with anti-CTLA-4 was proved to be effective in patients with malignant pleural mesothelioma (MPM). However, the minority of patients benefit from this treatment. The lack of immunotherapy efficacy in the majority of patients with mesothelioma can be explained by the fact that mesothelioma is a tumor with an “immune-desert” phenotype, meaning a non-inflamed tumor characterized by low T-cell infiltration. By administration of dendritic cells (DCs), which were cultured, activated, and exposed to antigens ex-vivo, this “immune-desert” phenotype might be turned into an “inflamed” phenotype. Previously, we performed and published three phase I trials using activated DCs, which support this concept. Here, we report the long-term survival of the patients treated with DCs in these three phase 1 studies. Methods: We collected the survival data of the phase 1 trials using DC therapy in patients with MPM. In the first two trials, DCs loaded with autologous tumor lysate were used, while in the third allogeneic tumor lysate was used to load the DCs (Mesopher). Results: Between 2006 and 2015, in the three studies combined, 29 patients with MPM were treated with DC vaccination. At data cut-off, the median OS was 27 months (95% confidence interval (CI): 21 – 47 months). OS at 2 years was 55.2% (95% CI: 39.7%-76.6%), OS at 5 years was 20.7% (95% CI: 10.1%-42.2%). Conclusions: The long-term follow up of MPM patients treated with DC vaccination in the three separate phase 1 trials show a promising signal, with a 2-year OS of over 50% and a 5-year OS of over 20%. In addition, 2 patients are alive after 10 years of treatment. In our opinion, these findings show the potency of DC vaccination therapy in long-term activation of the immune system. DC vaccination therapy in patients with MPM is currently being investigated in a large, randomized phase II-III trial (NCT03610360) and in pancreatic cancer. Additional biomarker studies, as well as treatment combinations with for example ICI, could further improve the outcomes of DC-vaccination therapy. Clinical trial information: NCT02395679. [Table: see text]